This invention relates to apparatus for positioning a sensor in vivo, and more particularly to a probe advancement mechanism and a mating interconnection for positioning the distal end of a sensor probe a predetermined distance from the distal end of an indwelling catheter.
There are numerous medical procedures which require the precise positioning of the distal end of a sensor probe within a blood vessel or other body cavity. For example, it has been proposed to perform a blood gas analysis on hospital patients both during and after surgery by placing a probe having a blood gas sensor at its distal tip within the patient's blood vessel. The sensor may measure one or all of the partial pressures of oxygen (PO.sub.2) and carbon dioxide (PCO.sub.2), and the negative logarithm of hydrogen ion activity (pH), to give an indication of the patient s cardiac, respiratory and circulatory functioning, and the rate of metabolism. The sensors may be electrical, chemical, and/or optical.
Among the suggested techniques of in-vivo measurement has been the use of fiber optic probes. In a fiber optic probe, light from a suitable source travels along an optically-conducting fiber to its distal end where it undergoes some change caused by interaction with a component of the medium in which the probe is inserted or interaction with a material contained in the probe tip which is sensitive to (i.e., modified by) a component in the medium. The modified light returns along the same or another fiber to a light-measuring instrument which interprets the return light signal.
Fiber optic sensors appear to offer several potential benefits. A fiber optic sensor is safe, involving no electrical currents in the body, and the optical fibers are very small and flexible, allowing placement in very small blood vessels. The materials used, i.e., plastic, metal, and glass, are suitable for long-term implantation.
However, one of the difficulties with fiber optic sensors is the fragility of the optical fibers. The fibers must be threaded through a blood vessel or other body cavity, sometimes over long distances, without breakage of the fiber. Furthermore, the fiber tip must not injure or puncture the vessel wall. Still further, for accurate measurement with many types of blood gas sensors and other procedures, the sensor probe must be precisely positioned within the blood vessel or body cavity in order to achieve an accurate measurement.
It is an object of this invention to provide an apparatus for positioning a sensor probe in vivo at a predetermined position in the body.
Another object is to provide apparatus for advancing a sensor probe within a catheter of selected length so as to position the distal end of the probe a predetermined distance from the distal end of the catheter.
A further object is to position a probe in vivo without injuring the blood vessel or other body cavity in which the probe is positioned.
A further object is to position a probe in vivo without damage to the probe.
Still another object is to provide a system for in-vivo positioning of a probe in a catheter wherein a mating interconnection is provided between a catheter of selected length and a probe advancement means such that the probe can only be used with catheters of selected length.